A turbojet engine 1 typically comprises a nacelle which forms an opening for admission of a predetermined flow of air toward the engine itself. The turbojet includes one or more sections for compressing the air admitted into the engine (generally one low-pressure section 2 and one high-pressure section). The air thus compressed is admitted into a combustion chamber and mixed with fuel before being burned there. The hot combustion gases derived from this combustion are then expanded in different turbine stages (generally a low-pressure section and a high-pressure section).
One example of a fan 3′ and of a low-pressure compressor 2 conforming to the prior art are illustrated in FIG. 3.
The fan 3′ comprises a fan disk 10′ provided with blades 3a′ on its periphery which, when they are placed in rotation, drive air into the turbojet. The fan disk 10′ is supported by a drive shaft of the low-pressure compressor 2′, which is centered on the axis of the turbojet by a series of bearings, supported by support parts connected to the fixed structure of the turbojet.
The low-pressure compressor 2′, for its part, comprises fixed vanes integral with a partition casing and movable blades integral with a drive drum 4 (known to persons skilled in the art as a “booster”) to compress the primary flow circulating from upstream to downstream in the turbojet. The drive drum 4 is for example fixed upstream of the fan disk 10′ by means of a bolted connection, and is driven in rotation by the fan disk 10′ about the axis of the turbojet.
The fan disk must consequently ensure the operability of the drive drum, that is be sufficiently flexible to guarantee maintaining the drive drum in position and control its radial behavior to ensure the tip clearances of the blades, while being sufficiently rigid to satisfy the fan blade loss criterion (or “fan blade out”).
Indeed, breakage of a fan blade 3a can result accidentally during operation. There follows a considerable unbalance on the drive shaft 2 of the fan 3, which generates loads and vibrations on the bearings, transmitted by their support parts to the fixed structure of the turbojet.
In order to be able to dimension the structure of the turbojet in a lighter and less costly fashion, the prior art teaches, as for example in patents FR 2,831,624 and FR 2,752,024, to provide for a turbojet 1 to be decoupled, including a system for decoupling one or more bearings. This, upon the appearance of an unbalance on the drive shaft, the unbalance forces are converted into longitudinal forces by the support part of the bearing. However, the fan disk being fixed to the drive shaft through a bolted flange 5′, the loads which pass into the fan disk and into the drive shaft then become very large at the connection in the event of decoupling. Such attachment by bolting is then not sufficiently rigid to withstand the loads which would result from the fan blade out.
It has also been proposed to modify the shape of the fan disk. Nevertheless, these shapes are generally bulky and heavy and/or do not allow flexibility and rigidity constraints required to both ensure operability of the drive drum and resist loads.
Document US 2012/0275921 proposes a fan disk conforming to the preamble of claim 1. However, the configuration of this disk has considerable bulk and mass. Document EP 1 970 537, for its part, which is in the Applicant's name, describes a fan disk having a junction wall extending radially with respect to an axis of the turbojet. However, this orientation of the junction wall has the consequence of concentrating the loads in a localized area of the fan disk, which limits the ability to withstand the loads of the disk, particularly during the fan blade out.